Homes and workplaces receive different types of data in different data formats for a variety of applications. For example, a home may receive data from satellite or terrestrial sources comprising High Definition Television (HDTV) broadcasts, Multi-point Microwave Distribution System (MMDS) broadcasts, and Digital Video Broadcasts (DVB). A home may also receive data via telephone (e.g. the Internet) and coaxial lines (e.g. cable TV) and from domestic sources such as PCs, Digital Video Disk (DVD), CDROM, VHS and Digital VHS (DVHS.TM.) type players and many other types of sources. Consequently, there is an increasing need for a Conversion system capable of accepting data in different data formats, from a plurality of different sources and that is capable of merging the data and converting it to a selected output data format for transmission on a selected transmission channel. Such a Conversion system is needed to support data processing activities including editing, storage and transmission for multi-media applications.
In such a Conversion system, the input data from multiple sources is in the form of packetized digital data. Input data from other sources e.g. analog video broadcasts, is converted into packetized digital data for processing in the Conversion system. However, there are a number of problems in merging and converting multimedia packetized digital data from different input format sources into a selected output data format. For example, an important factor in determining the way data from one or more different input sources may be merged and re-packetized is the range of data rates that is permitted by a receiving device or by the coding requirements of the desired output signal format.
The desired output data format typically imposes both a minimum and a maximum data rate limit in order to prevent underflow or overflow of an input data buffer in a receiving device. The data rate of the output format is also constrained by the bandwidth characteristics of the transmission channel. Consequently, it is necessary to re-code and re-packetize the input data in a manner that meets these data rate constraints. Other constraints on the format conversion of multimedia input data arise from differences in coding characteristics between the input data format and desired output data format. These coding characteristics include timing, error correction, conditional access and coding type characteristics. The problems involved in merging and converting digital data from different input format sources into a selected output data format are addressed by a system according to the present invention.